{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE Trustworthy #-}
-- | Primitives to convert between Float/Double and Word32/Word64
-- | This code was copied from `binary`
-- | This module was written based on
--   <http://hackage.haskell.org/package/reinterpret-cast-0.1.0/docs/src/Data-ReinterpretCast-Internal-ImplArray.html>.
--
--   Implements casting via a 1-element STUArray, as described in
--   <http://stackoverflow.com/a/7002812/263061>.
module Data.FloatCast
  ( floatToWord
  , wordToFloat
  , doubleToWord
  , wordToDouble
  ) where

import Data.Word (Word32, Word64)
import Data.Array.ST (newArray, readArray, MArray, STUArray)
import Data.Array.Unsafe (castSTUArray)
import GHC.ST (runST, ST)

-- | Reinterpret-casts a `Float` to a `Word32`.
floatToWord :: Float -> Word32
floatToWord x = runST (cast x)
{-# INLINE floatToWord #-}

-- | Reinterpret-casts a `Double` to a `Word64`.
doubleToWord :: Double -> Word64
doubleToWord x = runST (cast x)
{-# INLINE doubleToWord #-}

-- | Reinterpret-casts a `Word32` to a `Float`.
wordToFloat :: Word32 -> Float
wordToFloat x = runST (cast x)
{-# INLINE wordToFloat #-}

-- | Reinterpret-casts a `Word64` to a `Double`.
wordToDouble :: Word64 -> Double
wordToDouble x = runST (cast x)
{-# INLINE wordToDouble #-}

cast :: (MArray (STUArray s) a (ST s),
         MArray (STUArray s) b (ST s)) => a -> ST s b
cast x = newArray (0 :: Int, 0) x >>= castSTUArray >>= flip readArray 0
{-# INLINE cast #-}